Currently VSS dll/tlb files for use in w32 builds are only built as a
result of having been added to the general 'tools' target alongside
qemu-ga. This is fine for default make target, but if we build
qemu-ga directly via `make qemu-ga.exe`, the VSS files are not
created.
Fix this by moving the VSS dependencies to qemu-ga.exe directly.
With this move we can move the VSS files back out of 'tools',
and drop the extra handling from MSI target in Makefile.
Now we can build qemu-ga MSI package with:
./configure ...
make qemu-ga.exe
make msi